Fair usage policy

I have a premium uncapped account, that is supposed to be un-throttled and unshaped. Yet near the end of the month I get a 'fair usage policy' message and my connection is cut of. I have queried Telkom on this matter a number of times and have received no response. They claim that my usage effects other users and I should upgrade my account to a business account. That was the reason for the premium account in the first place 5 years ago. This was not part of the agreement or specified in my contract with Telkom.